1. Field of the Invention
The present invention relates to an illumination device for the interior of a vehicle. Particularly, it relates to an illumination device disposed in a roof portion of the interior of a vehicle so as to be used for illuminating the interior of the vehicle or an illumination device provided in the interior of a vehicle, the interior of an airplane or the like, for example, to be used as a reading light for illuminating a place close to occupant's hands.
2. Related Art
For example, in a roof portion of the interior of a vehicle such as a car, an illumination device (room lamp) for illuminating the interior of the vehicle is disposed for the purpose of improving safety when an occupant gets into the vehicle or out of the vehicle in the night or the like. In such an illumination device, a bulb is generally used as a light source. A light-transmissible cover is disposed on the light emission side of the bulb, so that the bulb light illuminates the interior of the vehicle through the cover.
In the related-art configuration, the cover is cut to a desired shape for the purpose of diffusing light. Though light is diffused to a certain degree by the cover, the form of illumination of light depends wholly on the light-emitting characteristic of the bulb. Accordingly, there is an illumination form in which illuminance is high in a place close to the light source (bulb) but becomes lower in a place farther from the light source. That is, illuminance varies widely in an illuminated range. In such an illumination form, it is impossible to grasp the position of a seat accurately or improve visibility at the occupant's step or the like sufficiently though an occupant can roughly grasp the interior of the vehicle when the occupant gets into the vehicle or out of the vehicle in the night or the like.
On the other hand, the directivity of the bulb light is so low that a relatively wide range is illuminated by the light. It is difficult to illuminate a necessary area precisely when an occupant in the passenger seat or in the rear seat needs a light while the vehicle is running. That is, there is fear that the surroundings of the necessary area may be illuminated to make the other occupants in the surroundings feel unpleasant.
Moreover, because the amount of heat generated in the bulb is large, the bulb is unsuitable for continuous use in an ON state for a long time. Hence, the related-art illumination device cannot be used for the purpose requiring long-time illumination, for example, as a reading light in the rear seat. The purpose of use of the related-art illumination device is therefore restricted within a narrow range.
Moreover, the illumination device heretofore generally used is of the type in which either a state of turning on the bulb (illumination state) or a state of turning off the bulb (non-illumination state) is selected automatically with the operation of a switch or with the opening/closing of any door. Hence, the form of illumination by the related-art illumination device is monotonous.
As described above, in the related-art illumination device using a bulb as a light source, there is room for improvement in the illuminating effect. In addition, when the bulb is used, it is undesirable that ambient parts (such as a cover) are disposed in proximity to the bulb because of the large amount of heat generated in the bulb switched on. This is a cause of hindrance to reduction in size.
A fluorescent lamp may be used as another light source. It is however necessary to provide a boosting circuit for driving the fluorescent lamp with a high voltage. There is fear that the boosting circuit may generate electric noise or magnetic field to exert influence on ambient parts.
On the other hand, there is a demand for the provision of an illumination device which can effectively illuminate a place close to occupant's hands when the occupant (in the rear seat or in the passenger seat) wants to read a book during the running of the vehicle. In response to the demand, the illumination device is required to be capable of being switched on for a long time without giving an unpleasant feeling to the user or other occupants around the user and without giving influence of heat on peripheral parts and apparatus as well as it is a matter of course that the illumination device is required to bring sufficient illuminance. It is further preferable that the illumination device is compact in consideration of the handling properties of the illumination device and the limited space in the interior of the vehicle. In addition, it is preferable that illumination can be performed by spotlight-like parallel light beams. According to illumination using parallel light beams, a predetermined region can be illuminated by a constant amount of light even in the case where the distance between the illumination device and a subject (e.g., a book) of illumination more or less changes. As a result, lowering of the illuminating effect can be prevented from being caused by vibration through the road surface during the running of the vehicle or by movement of the position of the illumination subject by the occupant himself or herself.
An LED is used spotlight-like illumination as a light source at present.
When the LED is used in place of the bulb or fluorescent lamp, the size of the illumination device can be reduced as well as the illumination device can be switched on for a long time without giving an unpleasant feeling to the user or other occupants around the user and without giving influence of heat on peripheral parts and apparatus. When, for example, a chip type LED is used, it is however impossible to form an illumination device capable of radiating parallel light beams by simply using the LED directly because diffused light is radiated from the LED. On the other hand, when a round type (lamp type) LED is used, it is possible to narrow range light to a certain degree in accordance with the shape of a sealing resin (molding member) but it is not easy to obtain parallel light beams. If parallel light beams are to be obtained, it is necessary to use a sealing member thick in the direction of the optical axis. For this reason, the requirements for reduction in size and thickness of the illumination device cannot be satisfied.
In the present circumstances, the illumination device using an LED is used not for illuminating a relatively wide range (e.g. not for reading) but for illuminating a narrow range (e.g., as a map lamp). The purpose of use of the illumination device using an LED is therefore limited.